Electric primary cell



Aug. 4, 1936. c. J. GORDON ELECTRIC PRIMARY CELL Original Filed April 5, 1954 LMW Patented Aug. 4, 1936 UNITED STATES PATENT OFFICE Original application April 3, 1934, Serial No.

718,769. Divided and this application September 25, 1935, Serial No. 42,038. In Britain April 6, 1933 4 Claims.

The object of this invention is to provide an improved primary cell of the kind in which magnesium is the electropositive electrode. Within the term magnesium", it is intended to include appropriate alloys in which magnesium is the predominating material. For such alloys to be suitable, it is necessary that the metals added to the magnesium should not be placed very far away from magnesium in the electrochemical series. As an example of an alloy which is appropriate, one containing about 7% of aluminium and from 1-2% of manganese and the remainder magnesium may be mentioned. The addition of aluminium within the range of 2-7% has been found to be an improvement on commercially pure magnesium. Where the word magnesium is used in the following specification and claims (unless the context indicates otherwise), it is to be assumed that it includes suitable al- 80 loys as well as substantially pure magnesium.

The invention relates to primary cells having I a layer of fibrous material lying between and in contact with the magnesium electrode and the second electrode and serving as a carrier for l the electrolyte.

The invention deals with the nature, form and disposition of the electrodes and the fibrous layer when assembled in their appropriate relationship for use in a cell. It does not deal with the U nature of the electrolyte. Electrolytes suitable for cells embodying the present invention are described in and form the subject of my co-pending application Serial No. 42,039 filed September 25, 1935, which together with the present applica- 35 tion have been divided from my co-pending application Serial No. 718,769 filed 3rd April, 1934.

In accordance with the invention the fibrous layer is caused to project beyond the edges of the electrodes. By this means the layer is placed 40 in contact with air to an appropriate extent and the air is caused by the action of the layer to effeet the depolarization. The full theory of this action is not understood but it appears evident that it is the oxygen in the air which is essential for the depolarizing and that it can be conveyed along the layer to the place where depolarization occurs. To be efiective to realize the advantages of the present invention, the projection of the fibrous layer should extend outwards to a distance at least of the same order as the thickness of the layer and preferably somewhat greater and should extend along a substantial proportion of the periphery of the electrodes. This arrangement is particularly applicable where the elec- Great trodes are in the form of flat plates impervious to air.

The materials used as the electronegative electrodes will be chosen from their position in the electrochemical series and from their other 5 physical properties and general constructional and cost considerations. Copper, silver and platinum are suitable. The last two would naturally be used as thin deposits on some less expensive metal support, for instance, on copper. 0

For the fibrous layer, a material of open texture is used. Many fibres are suitable but have somewhat varying degrees of eiiectiveness. It is preferred to use cellulose fibres, such as wood wool or blotting paper. This material is inert 15 and readily obtainable and has been found to be particularly effective for the purposes in view.

In order to avoid cutting ofi air from the fibrous layer, the electrolyte must be fed to the fibrous material without immersion of any important part of the area of the electrodes. The supplying of the electrolyte, in accordance with this condition, can be eiiected by placing the fibrous body in contact with a body of solidified material which is housed in an appropriate part of the container of the cell and is dissolved by the addition of water. By regulating the supply of water, some control of the action of the cell can be exercised. This is of importance in this type of cell since a slight chemical action on the magnesium electrode proceeds continuously while it is in contact with water and air.

It appears that, in this type of cell, it is the reaction between the water and the magnesium which provides the E. M. F. of the cell. The electrolyte serves the purpose of providing a conductive path between the electrodes.

The method of supplying electrolyte above described has the advantage that the electrolyte may be fed progressively from oneend oi the magnesium electrode to the other. This is of importance because, as the result of the action between the water and the magnesium electrode, a'comparatively large body of a non-conducting or poorly conducting compound is produced. By arranging the feed of the electrolyte to take place from the end of the electrode remote from the terminal, it can be ensured that the absorption of the electrode proceeds progressively from 50 the inner end of the terminal end and accordingly does not interfere with the continuity of the electrical connection. This method of supplying electrolyte also has the advantage that, as the reaction proceeds, the concentration of the elec- 55 trolytc increases and accordingly the reduction in the resistance 01 the conductive path produced by this means compensates aproximately for the increase due to other causes so that the internal resistance of the cell remains approximately constant, at least until the latest stage 01 the lite oi the cell is reached.

The invention wfll be further described in connection with an example of a cell embodying it, which is shown in the accompanying drawing.

Figure 1 shows in perspective and Figure 2 in end view, partly in section. a cell of a type suitable for heavy service.

Figure 3 shows in perspective the separated parts of this cell when the contents have been removed from the container.

The form of cell shown in this drawing includes as electrodes two sets of flat plates, the magnesium plates I and the other plates 2 which may, tor-instance, be of copper with or without a plating of silver or may be of steel with a plating of copper or silver. The two sets of plates i and 2 are interleaved as shown in Figure 2 and have between them sheets of blotting paper 3 which are applied by folding a large sheet completely round each of the plates as indicated in Figures 2 and 3. This causes the sheet to project beyond the plates into the air a distance greater than the thickness of the sheet at the two sides and top oi the plate. The plates terminate at the broken line 4 in Figure 3 and the sheets of blotting paper extend below as shown in that figure. Each plate has a lug on its upper end and these lugs form two oppositely disposed groups 5 and 6, the lugs indicated by 5 being those of the magnesium plates. Each of these groups of lugs is clamped by a terminal I. The assembly of plates and paper is housed in a metal container 8 which, as indicated in the drawing, has a form similar to that of a cover of a book. At that part corresponding to the back of the book, the sides unite to form a base chamber 9. The sides of the container have flanges Ill carried at an angle of about to the sides and arranged to meet when the container is in the closed position as shown in Figures 1 and 2. These meeting edges are provided with outwardly turned lips ll so that the flanges Hi can be held together by sliding slotted tubes I2 over these outwardly turned lips. The upper edges of the sides oi the container may be provided with similar flanges i3, having outwardly turned lips, which are held together by a slotted tube M. The side flanges enclose vertical spaces running the full height of the container above the base chamber 9. At the lower end of each of these spaces is a triangular extension ii of the end wall of the base chamber 9. This serves as a deflector and closes the greater part of the space.

From Figure 3, it will be readily recognized how the cell can be assembled. The group of plates with their wrappings is lowered into the container while it is in the open position shown in that flgure and is located in position by passing pins l1, formed of insulating material, through one pair or holes I8 in the side wall of the container and through holes is in the group of plates. The container is then closed. The flanges l0 and II are thus brought together and the container is secured in the closed position by sliding the slotted tubes i2 and it into place. The pins I! are then pushed through the holes 18 in the opposite side of the container and are secured by split pins passed through their projecting ends. When thus assembled, the lower ends oi the blotting paper wrappings l extend below the plates into the base chamber 0. This chamber contains a pad 20 consisting mainly or soluble electrolyte material. The cell is made active by pouring water into the base chamber. This can readily be effected by way of the spaca enclosed by the side flanges l0 and the deflectors I6. When the chamber 9 is fllled with water, the electrolyte material will be dissolved and the solution will be carried up by the layers of blotting paper into the spaces between the two sets of plates. The cell will accordingly be complete and current can be taken from it. This will continue until the whole of the water has been used up. The action of the cell may be carried on further by replenishing the water from time to time until the whole 01 the electrolyte material has been dissolved.

In the course of the working 01 the cell, the magnesium plates are destroyed, a comparatively large volume of compound being produced. By feeding the electrolyte from the bottom of the plates upwards, it results that the action on the magnesium is at flrst most intense at the lower parts and gradually extends to the upper parts. Accordingly the deposit of compound which is formed in the early stages of the operation of the cell is in the lower part 01 the container and extends only gradually to the upper part so that the action of the active portion of the cell is not materially interfered with by the production of a badly conducting body by the chemical action therein since this body is not placed directly in the path of the current.

It will be understood that the casing of the.

cell should be made of or coated with the same material as the working surface of the plates 2 so that no electrolytic action can take place between the container and these plates. It may be advantageous to connect the group of plates 2 with the container so that the latter forms part of the electronegative element of the cell.

It will be seen that the edges of the layers of paper 3 extend into the spaces enclosed by the flanges in at the sides of the container and are there in contact with air. This has an important eflfect in assisting the depolarizing action which these layers exert.

Where the sides of the container 8 Join the walls or the base chamber 9, a bent rib 2i is formed which serves as a spring hinge tending to hold the sides in the positions shown in Figure 3 but permitting them to be moved easily into the positions shown in Figure 1. Since the side walls of the container are of comparatively thin metal and are held together only at the edges, it is possible for a certain amount of expansion of the volume of the container to take place by the bulging outward or the lower and middle parts of the sides. This will serve to accommodate any expansion of the contents which may occur as the chemical action on the magnesium proceeds.

The amount of electrolyte material which is placed in the base chamber 9 will generally be calculated so asto suflice for the life of the cell, which is determined by the complete utilization of the magnesium plates up to the limit of practical working. when the cell is-exhausted, the container 8 can readily be opened and the contents removed. A new pad of electrolyte material can be placed in the chamber 9 and a new set of plates can be put in position in the upper part of the container so that the battery can readily be put into service again. The magnesium 76 plates 5' will have been almost completely destroyed in the working life of the cell but the other plates can be utilized repeatedly by being built up with other sets of magnesium plates and blotting paper layers to produce a plate assembly as shown in Figure 3 ready for insertion in a container.

This type of cell gives an open circuit voltage of about 1.3, the exact value depending upon the metal used for the electronegative plates. It can supply a current at the rate of about 1 amp. for each square inches (640 square centimetres) of surface of magnesium plates. This type of cell provides a large surface in a comparatively small volume and weight. The polarization of the cell is negligible for all reasonable current values and even after wrongful use, such as short-circuiting, the cell becomes very rapidly and completely depolarized.

I claim as my invention:-

1. A primary cell comprising. an electrode formed of at least one plate of magnesium, a second electrode also in plate form, fibrous material interposed as a layer between the electrode plates and projecting at the edges thereof and serving as a carrier for the electrolyte and for air for depolarizing and a case serving to house the assembly of plates and fibrous material and having in the base a chamber into which the fibrous material dips and from which it can be supplied with an electrolyte without immersion of the plates, the case having at each side spaces running the full height of the plates and serving for leading air to the fibrous material, parts or which project from the plates into these spacesand therein contact with the air.

2. A primary cell comprising an electrode formed of at least one plate of magnesium, a second electrode also in plate form, fibrous material interposed as a layer between the electrode plates and projecting at the edges thereof, the

projecting portions being in contact with air and the layer of fibrous material serving as a carrier for the electrolyte and for air for depolarizing and a case serving to house the essembly of plates and fibrous material and having in the base a 5 chamber into which the fibrous material dips and from which it can besupplied with an electrolyte without immersion of the plates,'the said case having a form approximating to that of the covers of a book, the part corresponding to the back 10 of the book forming the chamber from which the electrolyte is drawn and the sides of the covers being flanged so that they meet, means being provided to hold these flanges together.

3. A primary cell of the type having its electro- 1 motive force generated by the action of water on magnesium, comprising an electrode of magnesium, a second electrode, and a layer of fibrous material of open texture between and in contact with the two electrodes and projecting beyond 20 the edges of the electrodes, the projecting portions of the layer being in contact with .air and the layer serving as a carrier for electrolyte and for air for depolarizing. I

4. A primary cell comprising an electrode 25 formed of at least one plate of magnesium, a second electrode also in plate form, fibrous material interposed as a layer between the electrode plates and projecting at the edges thereof, the projecting portions being in contact with air and the fibrous layer serving as a carrier for the electrolyte and for air for depolarizing, and a case serving to house the assembly of plates and I fibrous material, said case having means for conducting air to the. projecting portions of the 35 fibrous layer and comprising sides hingedly connected to a bottom chamber into which latter the fibrous material dips and from which it can be supplied with an electrolyte without immersion of'the plates.

CHRISTIAN JENSEN GORDON. 

